1. Field of the Invention
The present invention relates to a flicker correction apparatus and flicker correction method, and more particularly, to a flicker correction apparatus and flicker correction method which correct a flicker component contained in an image sensed under a light source whose brightness periodically changes.
2. Description of the Related Art
Conventionally, an image sensing apparatus using a solid-state image sensor of X-Y addressing type, such as a CMOS image sensor, is commercially available. When shooting is performed using such an image sensing apparatus under the illumination of, for example, a fluorescent lamp or tungsten-filament lamp whose brightness varies in synchronization with the power supply frequency, the sensed image may have periodical bright and dark patterns in the vertical direction. This phenomenon, which is called flicker, occurs due to the difference between the commercial power supply frequency and the vertical sync frequency of the image sensing apparatus.
A method of suppressing such flicker is known, in which if the power supply frequency is, for example, 50 Hz, the shutter speed is fixed at 1/100 sec, thereby uniforming the exposure light amount in the lines and frames. However, since the shutter speed is fixed in this method, the degree of freedom of exposure control decreases.
Japanese Patent Laid-Open No. 2000-23040 discloses an image sensing apparatus which suppresses flicker by causing a photometric element provided independently of an image sensor to measure the flicker waveform of a fluorescent lamp and controlling the gain of a video signal output from the image sensor based on the flicker waveform.
Japanese Patent No. 3823314 discloses an image sensing signal processing apparatus which allocates a plurality of flicker detection regions by dividing an image in the direction of vertical scanning lines, detects luminance in each detection region, and calculates the luminance data difference between two preceding and succeeding frames in each detection region, thereby extracting and correcting flicker components.
However, the image sensing apparatus described in Japanese Patent Laid-Open No. 2000-23040 needs to have the photometric element for flicker detection in addition to the CMOS image sensor. In the flicker detection method described in Japanese Patent No. 3823314, if the object or camera moves, it is difficult to discriminate between the motion component and the flicker component in the sensed image, resulting in a decrease in the flicker detection accuracy and the flicker correction accuracy. Additionally, the sensed image may contain color information inappropriate for flicker detection. The flicker correction accuracy degrades in such an image.